Mold coating



Patented Aug. 17, 1937 MOLD COATING Howard C. Vance, Detroit, Michassignor, by

mesne assignments,

to Eaton-Erb Foundry Company, Vassar, Mich, a corporation of Michigan NoDrawing. Application October 30, 1931i,

. Serial No. 572,227

. Claims.

The specific object of my invention is to increase the life of cast ironor cast iron alloy molds such as used in production of iron castings.

The general object is to increase the life of 5 metal molds. Moldcoatings heretofore in use have been in two classes. (1) Refractorycoatings which were applied to the surface of iron molds such as shownin Meloche's Patent No. 1,492,694. (2) Coatings consisting of volatilesubstance. The volatile substances gave protection for a limited numberof castings but required re.- newing frequently. Neither of these twotypes of coatings has been altogether satisfactory. The refractorycoatings were porous and permitted the oxygen of the air to penetrate tothe metal in the moldand to oxidize it and thus destroy the mold.

This invention involves the protecting of the surface of a cast ironmold by providing a thin integral coating of aluminum iron alloy whichisimpervious to the oxygen of the a r. In practice the coating accordingto this invention is employed in conjunction with a refractory coatingsuch as described in the above-mentioned Meloche patent. The coatingaccording to the present invention is produced by first sand blastingthe surface of the cast iron mold or cleaning by other means toeliminate all grease etc., and slightly to roughen the surface, thenspraying molten aluminum onto the face of a cast iron mold to form acoating having a thickness of from .007 to .011'

40 the heating process the aluminum, being protected from air, does notoxidize, but alloys with the iron to form a permanent coating which isnot destroyed by the heat of the grey iron castings which may be pouredrepeatedly into such molds without the coating requiring to be renewed.The same method may be applied to protect a steel mold or a copper moldwith which aluminum alloys freely. The object of the application ofpotassium silicate is to insure that when heated the aluminum isprotected from the action of air,-to hold the aluminum in place untilthe alloying process has been completed, and to insure that the molditself heats up before the aluminum.

In the absence of the thin coating of potassium silicate or itsequivalent, when the mold is placed in the oven to be baked, not onlywill the aluminum be oxidized before it is alloyed with the iron, but itwill melt and run off and segregate in pockets; the desired uniformcoating of aluminum will not be produced and the dimensions of the moldwill be changed.

The aluminum iron alloy which is formed on the surface of the mold has ahigher melting point than the cast iron and increases the heat resistingqualities of the mold. As cast iron has a. relatively low melting pointand poor heat resisting qualities, it is most desirable to raise both ofthese in order the prolong the life of the mold. The life of the moldcan be still further prolonged by using this coating of aluminum ironalloy in conjunction with the Meloche coating described in the abovecitedv patent and also in Patent No. 1,453,593, which patents teach"that a thin solution of sodium silicate in water, having'finely dividedfire clay in suspension, is applied to a heated metal mold until a thinrefractory coating of fire clay bonded with silica gel forms on thesurface of the metal mold. Finally during the operation of the molds arelatively thick coating of lamp black is applied, which coating isremoved and renewed between each casting.

'As mentioned above, the aluminum coating can be applied to an iron moldand also to molds formed of alloys of iron and nickel, and iron andchromium.. This coating can also be applied to copper molds and'moldsformed of alloys of copper and tin (bronze) because aluminum alloys withcopper as freely as it does with iron.

What I claim is:

1. The method of protecting the surface of a cast iron mold by sprayingon the surface of the mold a layer of'from .007 to .011 of an inch .ofaluminum, then brushing the surface of the layer of aluminum with asolution in water of a soluble silicate and placing the mold in anannealing furnace at a temperature in excess of 1650 Fahrenheit.

2. The method of protecting the working surface of an iron mold, whichmethod comprises coating the working surface of the mold with anadherent layer of aluminum, protecting the sure face of the aluminumwith'a-temporary coating consisting of a solution in water of a solublematerial having a melting point in excess of 1750 Fahrenheit and thenheating the mold in an annealing furnace at a temperature of at least1650 Fahrenheit.

3. The method of protecting the surface of an iron mold by spraying onthe surface of the mold a layer of from .007 to .011 of an inch ofaluminum, then brushing the surface of the layer of aluminum with asolution in water of a soluble silicate and placing the mold in anannealing furnace at a temperature in excess of 1650 Fahrenheit.

4. The method of protecting the surface of a metal mold by sprayingonthe surface of the mold a layer of from .007 to .011 of an inch of valuminum, then brushing the surface of the layer of aluminum with asolution in water of a soluble silicate and placing the mold in anannealing furnace at a temperature in excess of 1650 Fahrenheit.

5. The method of protecting the working surface of when mold, whichmethod consists in: covering the working surface of the mold withaluminum; protecting the surface of the aluminum with a temporarycoating of a. material having a. melting point about 1750 Fahrenheit;and heating the protected mold at a temperature of at least 1650Fahrenheit, in such a manner that the temporary coating protects thealuminum against oxidization, holds the aluminum in place until alloyedwith the iron of the mold and causes the mold itself to be heated priorto the aluminum.

